Re: duration-problem while using make-sequential-music

[David Kastrup]

Thomas Morley <address@hidden> writes:

> Hi,
>
> trying to write a function to construct and mix/remix some music via
> `make-sequential-music' I noticed the following boiled down problem.
>
> The \xyz-function below should return a whole note for { b }

Why?

> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> \version "2.14.2"
> \version "2.15.43"
>
> xyz =
> #(define-music-function (parser location) ()
> (make-sequential-music (list
>       #{ a1 #}
>                 #{ b #})))

>From Changes:

   * The construct `#{ ... #}' can now be used not just for
     constructing sequential music lists, but also for pitches
     (distinguished from single note events by the absence of a
     duration or other information that can't be part of a pitch),

> Instead a cryptic log-message is printed:
>
> GNU LilyPond 2.15.43
>
> /home/harm/lilypond-git/build/out/share/lilypond/current/scm/music-functions.scm:35:14:
> In procedure ly:music-property in expression (ly:music-property mus
> (quote types)):
> /home/harm/lilypond-git/build/out/share/lilypond/current/scm/music-functions.scm:35:14:
> Wrong type argument in position 1 (expecting Music): (#<procedure
> embedded-lilypond (parser lily-string filename line closures)> parser
> " a1 " "various-tests.ly" 95 (list))

That looks more like '( #{ a1 #} ... rather than (list #{ a1 #} ...
this is the unevaluated form.  I get instead for

xyz =
#(define-music-function (parser location) ()
(make-sequential-music (list
        #{ a1 #}
                #{ b #})))
\xyz

-*- mode: compilation; default-directory: "/tmp/" -*-
Compilation started at Mon Aug  6 05:50:16

lilypond /tmp/ccc.ly
GNU LilyPond 2.15.42
Processing `/tmp/ccc.ly'
Parsing.../usr/local/share/lilypond/2.15.42/scm/music-functions.scm:35:14: In 
procedure ly:music-property in expression (ly:music-property mus (quote types)):
/usr/local/share/lilypond/2.15.42/scm/music-functions.scm:35:14: Wrong type 
argument in position 1 (expecting Music): #<Pitch b >

Compilation exited abnormally with code 1 at Mon Aug  6 05:50:17

> (with "2.14.2" the { b } defaults to a quater.)
>
> Intended is that the duration should change only if explicit forced.
>
>
> What am I missing?

Each #{ ... #} is executed in its own parser copy.  There is no useful
"default duration", so you should give an explicit duration anyway.  For
that reason, #{ b #} is a reasonable shortcut for specifying a naked
pitch.  Calling make-sequential-music is a low-level construct.  If you
really want this kind of thing to work, you can use

#{ $@(list #{ a1 #} #{ b #}) #}

But since the outer parser (which now sees a pitch second which it turns
into a note event in this place) still has not seen an explicit
duration, you'll get a quarter note anyhow.

-- 
David Kastrup